ST72411R datasheet(21/71 Pages) STMICROELECTRONICS

21 / 71 page

ST72411R

21/71

3.3 MAIN CLOCK CONTROLLER SYSTEM (MCC)

The MCC block supplies the clock for the ST7

CPU and its internal peripherals. It allows to man-

age the SLOW power saving mode acting on the

SMS bit of the Miscellaneous register (MISCR)

and the Main clock-out capability acting on the

CKD and CKAFOEN bits of the Smartcard Supply

Supervisor Control Register (SSSCR).

The main clock of the ST7 can be generated by

two different sources (see Figure 17):

an external source

an internal RC oscillator

The device is normally operated using an integrat-

ed 7.16MHz oscillator, meaning 3.58MHz operat-

ing frequency. However, an external clock can be

applied, up to 8MHz (4MHz operating frequency).

The

clock

source

selected

through

the

OSC_SEL pin status.

([ W

HUQDO&O

RFN6 RXUFH

The OSC_SEL pin status selects the External

Clock capability when it is tied to VDD. In this

mode, a clock signal with ~50% duty cycle has to

drive the OSCIN pin (see Figure 15).

,QW

HUQDO5& 2VFLOODW

RU6RXUFH

The OSC_SEL pin status selects the Internal RC

clock source capability when it is tied to VSS (see

Figure 16).

Note that OSC_SEL pin contains a pull-down

which allows to leave OSC_SEL in high imped-

ance in the application when the internal oscillator

is selected. This is mandatory for using the Re-

mote In Situ Programming feature.

Figure 15. External Clock

Figure 16. Internal RC Oscillator

Figure 17. Main Clock Controller (MCC) Block Diagram

OSCIN

OSC_SEL

EXTERNAL

ST7

SOURCE

VDD

OSCIN

OSC_SEL

ST7

highZ

(internal pulldown is present)

DIV 2

SMS

MISCR

fOSC

fCPU

OSCIN

INTERNA L

RC OSCILLATOR

7.16 MHz

OSC_SEL

DIV 16

SMARTCARD

interface

LCD and TIMER

SSSR

CK_A

CKD

FOEN

DIV 2

I/O ALTERNATE

FUNCTION

SC_CK

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